Conventional aqueous brine fluids, like calcium bromide, which can have densities up to about 14.2 pounds per gallon (1.70 kg/L), are widely used in oilfield production as clear completion fluids, drilling fluids, packer fluids, and so forth. For some wells, downhole pressures can reach 30,000 psi (2.1×108 Pa). Such high pressures occur downhole at least in the Gulf of Mexico, and temperatures at the mud line in the Gulf of Mexico can reach 40° F. (4.4° C.). As a general observation, each 10,000 pounds per square inch (6.9×107 Pa) increase in pressure can increase the crystallization temperature of an aqueous brine by about ten Fahrenheit degrees (about 5.6 Celsius degrees).
Typical aqueous brine fluids include calcium bromide having densities up to about 14.2 ppg (1.70 kg/L). A calcium bromide aqueous brine of about 14.2 ppg (1.70 kg/L) density has a true crystallization temperature of less than 10° F. (−12.2° C.). Calcium bromide aqueous brines having densities as high as 15 ppg (1.8 kg/L) can be made; however, these solutions have a true crystallization temperature of about 61° F. (16.1° C.). These higher density calcium bromide aqueous brines are not suitable for use in some downhole applications, such as conditions often found in the Gulf of Mexico, because precipitates will form in these higher density calcium bromide aqueous brines due to their relatively high true crystallization temperatures.
Zinc-containing calcium bromide aqueous brines of high density, e.g., about 14.5 pounds per gallon (1.74 kg/L) or greater, are easily obtained by blending enough zinc bromide into the calcium bromide aqueous brine to reach the desired density value. Zinc-containing calcium bromide aqueous brines have true crystallization temperatures that are usually about 20° F. (−6.7° C.) or lower, making these zinc-containing brines more suitable for downhole use. However, inclusion of zinc necessitates increased reporting to government agencies for environmental reasons, resulting in more costly environmental mitigation measures. For example, zinc is regulated as a Priority Pollutant by the United States Environmental Protection Agency (EPA).
Hence, there is a need to develop high density aqueous brine fluids that are zinc-free, and that have true crystallization temperatures that are suitably low for downhole use.